Lukewarm radiators

[jimmyharris80]

Hi All,

I have a couple of rads within our property that are running luke warm, I'd be surprised if they're heating the surrounding air at all! Two barely heat up, the other is half warm/half hot.

I’ve bled each rad and also closed all rads except the problem ones with the heating on and thermostaic valve on max to try and push flow through them but it hasn’t rectified the problem.

Boiler is a Baxi DuoTec Combi HE and I believe it was fitted in 2011 (before we bought the property). There is a total of 7 rads running off the boiler, 4 function just fine, 3 are not quite right.

All rads are new (2011) and all have thermostatic valves, pipework into rads above floor is new but unsure if boiler was plumbed into old pipework under the floorboards. Floorboards have solid oak flooring layed over the top so pulling that up to find out is not really an option!

Does anyone have an idea what the issue could be and options to rectify?

 

[naanbread]

Hi All,

I have a couple of rads within our property that are running luke warm, I'd be surprised if they're heating the surrounding air at all! Two barely heat up, the other is half warm/half hot.

I’ve bled each rad and also closed all rads except the problem ones with the heating on and thermostaic valve on max to try and push flow through them but it hasn’t rectified the problem.

Boiler is a Baxi DuoTec Combi HE and I believe it was fitted in 2011 (before we bought the property). There is a total of 7 rads running off the boiler, 4 function just fine, 3 are not quite right.

All rads are new (2011) and all have thermostatic valves, pipework into rads above floor is new but unsure if boiler was plumbed into old pipework under the floorboards. Floorboards have solid oak flooring layed over the top so pulling that up to find out is not really an option!

Does anyone have an idea what the issue could be and options to rectify?

It sounds to me like you may have a slight restriction within the system itself. It wont be the boiler thats the issue on the basis that some of the rads work, it could possibly be the pump on its way out but its less likely if there is some warmth in the rads. Whats the quality of water like? does it seem quite dirty with small metal flakes in it?
it might be worth cleaning a few of the radiators out to see if this cures the problem. Simply drain them down, take them into the garden and run the hose through them. You might have to get a professional in to do a chemical clean if its no better. I certainly wouldnt worry about ripping the flooring up just yet.

Im no expert on systems but this is where i would personally start. Its the cheapest as it will only cost your time. If anyone else can give more input it might help

I hope this helps

NB

 

[selmar47]

Some thermostatic valves have a pin that shuts the water off as the set temperature is reached. These can stick when the temperature drops, so try taking the two off the lukewarm rads and check the pins. A squirt of WD 40 and working them up and down with a pair of pliers usually frees them off. Other than that if you have a combi boiler, check the pressure is correct as too little water in the system could cause this problem. If the pressure is low, increase it via the filling loop and then re-bleed all the rads checking the pressure regularly to make sure the system stays filled with water.

 

[jimmyharris80]

Thanks both, I'll give some of those suggestions a go over the next couple of days and report back.

 

[jimmyharris80]

Hi all, back again! Checked all TRV's, removed the top and pins all push down and pop up, all working fine.

I've attempted to rebalance the system by shutting all rads off except the problem ones, and turning on one by one. As we moved in a year or so ago and theres flooring throughout I don't know which order the rads are from the boiler so balancing has been a bit trial and error, opening up the problem rads fully and turning down the working ones.

Rad in the living room is a lot warmer but red hot at the top and lukewarm at the bottom, both in and out pipes are red hot.

Other vertical rads in bedrooms are still not heating up properly, one is only lukewarm the other half hot/half cold and they take a long time to heat up. in and out pipes are red hot on both. Heat is getting into the bottom horizontal part of rad but not transferring up to other parts.

To compare when you open our towel rail in the bathroom you can feel the hot water enter in immediately and it's warm within a couple of mins.

Could it be sludge in the problem rads? Any ideas?

 

[Armo74]

If the rads are cold at the bottom and hot/warm at the top that is usually an indication that there could be a build up of magnetite.
Is the water clear when you bleed the rads?

 

[jimmyharris80]

Not completely clear no, leaves grey marks on the white cloth I'm using but wouldn't say the water was filthy.

Wouldn't say rad was cold at the bottom, just nowhere near as hot as the top.

 

[D_Hailsham]

vertical rads

Are all rads vertical?

If not, are all problem rads vertical?

Vertical rads often need the flow and return pipes connected a certain way round. Are they correct?

When balancing, remove all TRV heads and start with all lockshield valves 1/3rd turn open. Any adjustments should be minimal and time must be allowed for the system to rebalance (say 10 min).

 

[jimmyharris80]

No, not all of them, 3 vertical, 3 horizontal and a towel rail. No idea if the return and flow are the right way round or even if they need to be a certain way, only moved in just over a year ago and system was installed in 2009 by previous owner.

Vertical 1 (Lockshield right, TRV left) - works fine
Vertical 2 (Lockshield left, TRV right) - half hot/half cold
Vertical 3 (Lockshield left, TRV right) - barely heats up at all

All verticals have red hot in and out pipes and the bottom horizontal pipes are hot, just heat not transferring up the problem rads.

Horizontal 1 - works fine
Horizontal 2 - works fine, maybe a little cooler at the bottom than the top
Horizontal 3 - piping hot at top, lukewarm at bottom

Towel rail - works fine

Will give re-balancing another go and see if there's an improvement, last time round I had it running for at least 30 mins.

 

[Agile]

This is where a knowledge of the last two year's history would help a lot.

It seems you have a blockage in the bottom of some radiators.

A bucket test of the problem rads would also give useful imformation.

Tony

 

[D_Hailsham]

Vertical 1 (Lockshield right, TRV left) - works fine
Vertical 2 (Lockshield left, TRV right) - half hot/half cold
Vertical 3 (Lockshield left, TRV right) - barely heats up at all

Which side has the hotter pipe on each rad?

All verticals have red hot in and out pipes

There should be a noticeable difference in temperature between the in (flow) and out (return) pipes. If there is little difference, it means that the water is flowing though the radiator too quickly, so the LS valve needs to be closed more.

 

[Blagard]

The verticals rads that are not getting hot - Can they be mounted the other way up?

Because I understand some have baffles between the flow and return forcing flow around the radiator. It could be the rads were fitted upside down allowing water to pass from flow to return without circulating due to the top not having baffles.

 

[jimmyharris80]

Hi All – Right, so I’ve spent a fair few hours over the weekend trying a few things out. I drained down the system completely (water was pretty grey but I wouldn’t say it was filthy), topped up again with water and drained down once more (again water was grey but not too bad). Third time round I added some Sentinel X800 and flushed it through each rad in turn for 20 mins and left it running last night. Last night I drained the system fully again and the water is a lot dirtier, I then flushed it via the filling loop until clean water ran out of the drain down valve then topped up to 1.5 bar and bled all rads.

Agile – I would have done a bucket test if I had a spare pair of hands but all of our rads are pretty big and a 2 man job to whip them off without causing a mess, I could try this next weekend as the old man is round and can give me a had.

The three problem rads are a little better but are still taking a long long time to warm up even when flow is shut off to all other rads. We have 2 identical rads on opposite sides of the wall of bedroom 1 both behaving very differently:

Bedroom 1
Vertical 1 (Lockshield right, TRV left) - works fine – heats up in less than a few minutes when all other rads are shut off.
Vertical 2 (Lockshield left, TRV right) - takes at least 20 mins to warm up, right 3 verticals heat up quickly, the rest take a long time. Bottom left of rad near lockshield hardly heats up at all and rad makes a snap, crackle & pop (rice crispy!) type noise when I introduce flow into it via the fully opened lockshield.

Bedroom 2
Vertical 3 (Lockshield left, TRV right) – Alightly different model to the other two (see pics). Again, takes at least 20 mins to warm up and doesn’t get that hot even when all other rads are shut off, hotter at the top than the bottom and some cold spots in 1 or 2 of the 6 verticals as well

Lounge
Horizontal - A bit better but still takes a fair while to warm up (10 mins), the differential between the top and bottom is less than it was before but still noticeable.

In terms of the rads being the wrong way round. The rad in Bedroom 1 is reversible so it looks like the next option may be to switch it round back to front. The rad in Bedroom 2 however is not as it has a welded cross piece on the rear which would look horrible if I span it to the front! Would spinning this rad 180 degrees so top left is then bottom right fix it or would the flow still be the wrong way round?

I’ve added some images of the rads into my album, not sure if this helps at all!

//www.diynot.com/network/jimmyharris80/albums/

 

[D_Hailsham]

Make and model name of the vertical rads would be helpful.

 

[Agile]

If a vertical rad is hot at the bottom only close to the supply pipes then that's usually because its upside down!

They often have a restriction in the bottom to encourage the flow to go to the top!

Of course air in the top will also make it cold there too!

Tony